Yeast

The word
"yeast" comes from the Sanskrit 'yas' meaning "to seethe or boil". Yeast
is a living organism and is in the air around us. It is a member of
the fungus family and is a single-celled fungi of which there are about 160
different species. Baker's yeast as well as brewer's yeast belong to the
Saccharomyces cerevisiae species. Louis Pasteur in the 1850's is credited
with first discovering and understanding the fermentation process which led to
the development and cultivation of the yeast we use today.

Baker's
yeast, like baking powder and baking soda, is used to leavened baked goods
(breads, Danish pastries, brioche, croissants).
The difference between these two leaveners is that baking powder/soda react
chemically to produce the carbon dioxide that makes the baked goods rise.
Yeast, on the other hand, is a living organism and the carbon dioxide it
produces is the result of the yeast feeding on the dough.

Fresh yeast
is ivory colored with a yellowish hue and is soft and moist and should easily
crumble. Make sure it is fresh smelling and there are no dark or dried
places on the yeast. It is mainly used by professionals as it is
highly perishable and must be used within a short time of opening. It is sold
is .06 ounce foil packages and must be refrigerated. For longer term storage it can be
frozen. Compressed yeast contains about 70% moisture. It
needs to be proofed before using and should have a pleasant yeasty smell and be
foamy.

Dry yeast
is fresh compressed yeast that has been pressed and dried until the moisture
content is only about 8% which makes the yeast dormant. The granules only
become active again when mixed with a warm liquid. The advantage of dry
yeast is it has a much longer shelf life than fresh yeast and does not need to
be refrigerated. This makes it a favorite among home bakers.
The tiny, dehydrated, bead-shaped, sand colored granules are most often sold in
convenient small foil-lined packages weighing 1/4 ounce (7 grams) that have been
packaged under pressure. Always check the expiration date on
the package before buying. It is
also sold in 4 ounce jars but once opened, the yeast needs to be stored in the
refrigerator away from moisture, heat, and light because once yeast is exposed
to air it deteriorates rapidly.

There are
two types of dry yeast: regular active dry and rapid-rise.The two types of dry yeast can be used interchangeably. The advantage
of the rapid-rise is the rising time is half that of the active dry and it only
needs one rising.
However, you do sacrifice flavor and texture in order to save time as the yeast
does not have time to develop its own flavor.

You may
have noticed that in some recipes it calls for dissolving the yeast first in a
warm liquid and then adding this active yeast mixture to the flour. Other
recipes, however, call for the yeast first being added to the flour and then the
warm liquid is added. The dissolving of the yeast first in a warm liquid
is done to make sure the yeast is still fresh and active. This step really
doesn't need to be done though because of how reliable the dry yeast is today.
Also, the dry yeast has such a small granule size that it dissolves easily into
the dough without having to be reconstituted separately. Some bakers,
however, still feel that it is a good idea to test the yeast to make sure it is
still active before adding it to the flour.

Yeast
must have three things in order to grow: Moisture, Food, and Warmth.

To activate
yeast the first step is called proofing and is a way to test the yeast to
make sure it is alive and still active. This is accomplished by mixing the
yeast in a warm liquid. In order for yeast to become very active it needs
food. It's favorite food is sugar, simple sugars to be precise (glucose
and fructose). Some recipes call for adding granulated white sugar which
the yeast will break down into its simpler form. But in some bread recipes
where sugar is not used, flour can be added to the warm liquid and the yeast
will break down some of the starch in the flour to a simple sugar.

Once the
yeast, liquid, and flour are mixed together and distributed, the next step is to knead the dough. This step is done to aerate the dough and develops
the gluten (elasticity) in the flour. As you knead (press-fold-turn
action)
pockets of air are developed in the dough. The more you knead the smaller
and more numerous the pockets of air become. How the dough is kneaded will
determine the final texture of the bread. Dough with larger air pockets
will produce a bread with a coarser texture. Commercially made breads or
homemade ones that are kneaded by machine tend to have a finer texture than
breads kneaded by hand. You'll know when the dough has been kneaded enough
as it takes on a smooth and satiny appearance.

The next
step is the fermentation or rising of the dough. This is
where the dough is placed in a greased bowl and covered with plastic wrap or a
clean dish towel to avoid moisture loss and a dry, crusty surface from forming.
The dough is then left in a warm, draft-free environment to rise until about
double in size. The rising starts slowly as the yeast begins to feed on
the sugar. Carbon dioxide and alcohol are produced and the carbon dioxide
stretches and expands the existing air pockets in the dough and the dough starts
to rise. This is also where the bread's flavor is developed. A dough
that doesn't rise sufficiently will be very compact.

Once the
dough has doubled in size this signals the next step i.e. thepunching downof the dough. This 'punching down' is where the dough is deflated,
thereby releasing the large air pockets formed during rising and evenly
distributes the temperature and yeast throughout the mass of dough.
Depending on what you are making, at this point there may be a second rising.
Otherwise, the dough is shaped and placed in a pan and allowed to rise for a
shorter period of time.

The final
step is the baking of the bread. The temperature of the oven can
vary depending on the baked good. A sweet dough is normally baked at about
350 - 375 F (175 - 190 C). Other dough can be baked at a higher
temperature 400 - 425 F (205 - 220 C). During the first part of baking,
before the yeast is killed, the dough will rise as you get a last bit of carbon
dioxide being released and expanding the air pockets. Once the yeast is
killed and the interior of the baked good heats up enough, the dough will set.
The last part of the baking is where you get surface browning and this adds
flavor and texture to the baked good. Often times the surface of the baked
good is brushed with an egg wash (can also place a pan of hot water in the oven
or spray the baked good with water periodically during baking) before baking so
the crust will be nicely browned and glossy.

How long
the baked good stays fresh is dependent on the sugar content. French
breads that do not contain sugar have a very short shelf life. On the
other hand, a sweet dough that contains sugar can stay fresh for several days.

"Bread deals
with living things, with giving life, with growth, with the seed, the
grain that nurtures. It is not coincidence that we say bread is
the staff of life."

- Lionel Poilane

When yeast is used in baked goods (breads, Danish
pastries, brioche, croissants, etc.) it not only increases the volume
but also improves the texture, grain and flavor of the bread.

Sweet Yeast Dough needs to contain more yeast (can be
up to double the amount of yeast used in bread dough) because the extra
sugars in the dough tends to slow down the yeast.

1 cake of fresh yeast = 1 envelope of dry yeast

1 package of dry yeast = 1 scant tablespoon

1 package of yeast or 1 cake of fresh yeast will
leaven about 4 cups of flour

Proofing - the testing of the yeast to
make sure it is still active. This is done by dissolving the yeast
in a warm liquid to which sugar or flour have been added. This
mixture is then set aside for 5-10 minutes and should become foamy and
bubbly.

Note: If the dry yeast is added directly to the
flour, the liquid that is added is warmer than usual because the whole
mass of dry ingredients, as opposed to just the yeast, must be warmed in
order to activate the yeast.

Kneading- A technique used to combine and work a dough or
mixture into a smooth and pliable mass. In bread making, kneading
the dough also develops the gluten strands in the flour so it adequately
holds in the gases released by the leavener (yeast) to produce a bread
with good volume and texture. This technique can be done by hand,
using the press-fold-turn action, or using a food processor or electric
mixer with the dough hook.

References
cited may include a link to purchase the referenced book or item on Amazon.com.
Joyofbaking.com receives a commission on any purchases resulting from these
links.

This
website and the contents are not endorsed or sponsored by the owner of the
"Joy of Cooking" series of books or its publisher Simon & Schuster, Inc.
and is not related to the "Joy the Baker" books and website.
Video icons by Asher.

Content in any form may
not be copied or used without written permission of Stephanie Jaworski,
Joyofbaking.com. Students and non profit educators may use content without
permission with proper credit.